D.P. BRENNAN DEPARTMENT OF PHYSICS AND ENGINEERING PHYSICS THE UNIVERSITY OF TULSA

1. High Performance Computing and the U.S. Burning Plasma OrganizationNews from the Front Line of Fusion Simulations D.P. BRENNAN DEPARTMENT OF PHYSICS AND ENGINEERING PHYSICS THE UNIVERSITY OF TULSA PRESENTED AT THE HPC USER FORUM HOUSTON, TEXAS WEDNESDAY, APRIL 6, 2011

2. Outline The need for predictive integrated modeling of burning plasmas Challenge of joining several sub-disciplines with disparate physics USBPO is an organization dedicated to facilitating burning plasma science, and helps organize and disseminate research Fusion Simulation Program is a prime example of a nascent community wide integrated modeling effort The needs of fusion simulation are increasing – need for speed Summary

3. Predictive Modeling Effort in Burning Plasma Science extends from resolving puzzles in current experiments EXAMPLE: Experiment in the DIII-D tokamak (General Atomics, San Diego) shown, where core instability appears and terminates discharge. What causes the system to cross into instability, how can we control and prevent this? What are the main drivers? A combination of HPC, smaller desk top computation, and reduced modeling address these and many other questions.

4. Predictive Modeling Effort in Burning Plasma Science Basic onset can be explained, but the evolution to the onset, specific drive through onset, and evolution afterward, all difficult. Predictive modeling can lead to reduced risk and focused experimental tests. Accuracy involves coupling between physics drivers

5. Goals of the Computational Community in Burning Plasma Science • Attain a more profound physics insight of existing experimental results • Test, further understand and extend theory with numerical efforts • Address and resolve issues that stand in the way of ignition in burning plasma experiments • Identify solutions • Predictive modeling of specific experimental configurations in ITER • Provide a basis for analysis of successor experiments such as DEMO

6. Magnetic fusion codes predict instabilities and other plasma phenomena critical to ITER Disruption forces, RE, and heat loads during disruption Edge Localized Modes “sawtooth oscillations” Disruptions caused by short wave-length modes interacting with helical structures. Mass redistribution after pellet injection Interaction of high-energy particles with global modes S. Jardin (PPPL)

7. Challenges of fusion simulation • Basic description of plasma is 7D • f(x,v,t) evolution determined by nonlinear Boltzmann equation and Maxwell equations convection in space convection in velocity space Collisional relaxation toward Maxwellian in velocity space • Difficulties: • High dimensionality; nonlinearity; sensitivity to geometric details • Extreme range of time scales (electron cyclotron to wall equilibration): ~ O(1014) • Extreme range of spatial scales (electron gyroradius to machine size): ~ O(104) • Extreme anisotropy (mean free path parallel/perpendicular to B field): ~ O(108) D. Batchelor (ASCAC 06)

8. Fusion simulation sub-disciplines must be coupled Important processes couple all phenomena at all relevant time scales S. Jardin (PPPL) J.Van Dam (UT)

9. Integration between and across areas forms key element of this effort to addressed coupled phenomena • Examples: • Heat transport from MHD instabilities • Fast particle transport form MHD instabilities • Fast particle interaction with RF heating • Edge physics coupling with core physics Specific Example: Edge localized mode coupled to a core MHD mode with energetic particles xMHD ELM xMHD TM PIC df of energetic particles + + What are the stability boundaries and evolution as thermal energy increases and transport changes? => experimental observations

10. Origin: USBPO is national organization of scientists and engineers involved in researching the properties of magnetically confined burning fusion plasmas Mission: Advance the scientific understanding of burning plasmas and ensure the greatest benefit from a burning plasma experiment by coordinating relevant U.S. fusion research with broad community participation Recent “White Paper on Simulations for ITER” (August 2007) Written by USBPO Topical Group on modeling and simulation Argues that Fusion Simulation Project is an essential element in strategic planning for fusion energy science in the ITER era Submitted to new Fusion Energy Science Advisory Committee Planning Panel to identify issues arising in a path to DEMO, with ITER as a focus of that effort US Burning Plasma Organization (USBPO) http://burningplasma.org/home.html

11. Coordinating the US burning plasma effort DOE Office of Fusion Energy Sciences SC Assoc Director Research Division ITER and International Division US ITER Project Office Director US ITER Chief Scientist (USBPO Director) US ITER Chief Technologist (VLT Director) ITPA Virtual Laboratory for Technology USBPO Directorate Director Deputy Director Ass’t Director for ITER Liaison Research Committee USBPO Council (14 members) US Burning Plasma Organization Topical Group MHD Stability Topical Group Confinement/Transport Topical Group Boundary Topical Group Wave Interactions Topical Group Energetic Particles Topical Group Integrated Scenarios Topical Group Fusion Engineering Topical Group Modeling/Simulation Topical Group Operation/Control Topical Group Diagnostics

12. Fusion Simulation Project (FSP) • What is the FSP? • Computational initiative aimed at the development of whole-device, integrated predictive simulation capability focusing on ITER, but also relevant to major present and planned toroidal fusion experiments • Why is FSP needed? • Each pulse in ITER is expected to cost ~ $1M, so a reliable predictive simulation capability is needed to optimize discharge scenarios and control • Why start it now? • Challenging undertaking: will take time to develop, verify, and validate (V&V) such comprehensive simulations • SciDAC program has taken advantage of modern terascale computing facilities to develop high-performance computational tools to develop new insights into questions of fundamental importance in fusion plasma science • Emerging availability of petascale computing resources

13. FSP prototype centers (integration) • Center for Simulation of Wave Interactions with MHD (SWIM) • Brings together state-of-the-art extended MHD and RF codes to investigate the interactions of waves with MHD and the mitigation of instabilities • Develop Integrated Plasma Simulator (IPS) framework for coupling of any fusion code • PI: D. Batchelor (ORNL) • ORNL, Indiana U, Columbia U, General Atomics, CompX, U Wisconsin, MIT, NYU, LBNL, Lehigh U, Tech-X • Center for Plasma Edge Simulations (CPES) • Develop integrated predictive plasma edge simulation package applicable to burning plasma experiments; integrate edge gyrokinetics with extended MHD • PI: C. S. Chang (NYU) • CalTech, Columbia U, LBNL, Lehigh U, MIT, ORNL, PPPL, Rutgers, UC Irvine, U Colorado, U Tennessee, U Utah • Framework Application for Core-Edge Transport Simulations (FACETS) • Multi-physics, parallel framework application for full-scale fusion reactor modeling; initial focus is core-to-wall transport modeling • PI: J. Cary (U. Colorado, Tech-X) • Tech-X, LLNL, PPPL, ANL, UCSD, CSU, ORNL, ParaTools, General Atomics, Columbia U, LBNL, Indiana U, MIT, NYU, Lodestar

14. The representative suite of tokamak models includes a variety of temporal and spatial discretization schemes • Explicit PIC Modeling: GTS, VORPAL • Wave heating, Wall interaction • Core Transport: GYRO/NEO • Collisional Edge Plasma: BOUT++ • MHD: M3D-C1, NIMROD S. Kruger, J. Cary (Tech-X)

15. The glue: FACETS - coupling framework for Plasma Simulations • Coupling on short time scales • Inter-processor and in-memory communication • Implicit coupling Hot central plasma: nearly completely ionized, magnetic lines lie on flux surfaces, 3D turbulence embedded in 1D transport Cooler edge plasma: atomic physics important, magnetic lines terminate on material surfaces, 3D turbulence embedded in 2D transport Material walls, embedded hydrogenic species, recycling S. Kruger, J. Cary (Tech-X)

16. Fusion simulation “speed” increases due to hardware and algorithms S. Jardin (PPPL)

17. Dominant self-heating (exothermic) Flexibility in present-day experiments to control current, pressure, and rotation profiles by means of external RF power and neutral beams is dramatically reduced in a burning plasma experiment High performance requirements Sustained, simultaneous achievement of high temperature and density, good macroscopic stability, good confinement of plasma energy Robust plasma-wall facing components and diagnostics that can withstand high heat and neutron wall loadings New features in a burning plasma (1) • Long pulse length • Burning plasma experiment should have pulse length long compared to the current redistribution time (pulse >> CR) to investigate resistively equilibrated current and pressure profiles in the presence of strong alpha heating

18. Strong coupling The critical elements in the areas of transport, stability, boundary physics, energetic particles, heating, etc., will be strongly coupled nonlinearly due to the fusion self-heating Size scaling Due to much larger volume than present experiments, size scaling becomes important for confinement Large population of high-energy alpha particles Different behavior from thermal ions Affect stability and confinement New features in a burning plasma (2) Cross sections of present EU D-shape tokamaks compared to the cross section of ITER

19. Full burning plasma simulations will need ~O(106) speed increase D. Batchelor (ASCAC 06)

20. Summary HPC is a crucial part of our effort to advance burning plasma science. Experimental observations/analytic work/small jobs/big jobs steer and make up an HPC burning plasma science effort. The emerging paradigm involves large scale collaborative efforts to couple together physics models which describe different parts of the puzzle that will predict the outcome of burning plasma experiments. The USBPO helps to coordinate this community effort to advance our physics understanding of burning plasmas and help make fusion energy a reality. We live in an exciting place and time, where computational scientists are beginning to collaborate on massive projects to solve long standing puzzles via comprehensive cutting edge simulations.